(1) The Field of the Invention
This invention relates to adhesives. More precisely this invention relates to improved reactive fluid adhesives and activators for such adhesives.
(2) Description of the Prior Art
Polymerizable compositions are known which are believed to cure or harden by free radical polymerization of ethylenically unsaturated components of the composition. Reactive fluid adhesive compositions for example are known which cure at room temperature by addition polymerization of monomeric components to provide adhesive bonds between surfaces of various different materials. Reactive fluid adhesive compositions intended to cure between opaque, impervious, or other materials to form an adhesive bond may comprise one or more polymerizable acrylate or methacrylate ester monomers, a source of free radicals such as a peroxide, hydroperoxide, per ester or per acid, and an activator for interaction with the source of free radicals to initiate polymerization of the monomers at room temperature. The source of free radicals and the activator may be stored separate from each other before use of the adhesive. One of them may be incorporated in admixture with the monomers during storage, so that the reactive fluid adhesive composition includes two parts. The composition cures to form an adhesive bond when the two parts are brought together in absence of oxygen.
In one particularly convenient method of using reactive fluid adhesives, one part of the composition comprising the activator is applied to a surface to be bonded in the manner of a primer before the application of the other part of the composition comprising the polymerizable monomers and source of free radicals. This method allows the use of the adhesive composition without having to mix the two parts prior to application. The activator is conveniently one which can be used in non-stoichiometric quantities with respect to the monomers.
Certain known amine-aldehyde reaction products effective as activators in reactive fluid adhesive compositions are liquid materials having a certain degree of toxicity and offensive smell. In view of the increased emphasis on using non-toxic materials, adhesive compositions comprising an activator system having a more acceptable level of toxicity and smell has become particularly desirable. In providing such adhesive compositions, solid materials have been considered. However, solid activators remain present in the bond in their solid form and this feature is not desirable in adhesives of commercially acceptable performance characteristics. Additionally, amine aldehyde reaction products preferred for use as activators in the past have led to cured adhesive bonds which tend to discolor significantly under the influence of light. Any discoloration can be a disadvantage in adhesive bonds which are visible, for example in bonds between glass and other translucent or transparent materials. The present invention is addressed to the outstanding problems in the art discussed above and presents to the art novel improved adhesive compositions comprising activator materials of particularly desirable improved performance characteristics.